Good plan, but just a question... have you ever tested your smallest possible PWM duty to see how much current is generated on a locked motor? As with anything there are two ways to go about it... you can "just try it" or you can gather some system properties and get a design starting point... Its up to you... if you nail it quickly with your tuning method, great, otherwise we'll talk about some systematic approach to quantifying how the system works, then designing a control method from there.